It can be anything. Thats why you should consult your doctor,rather than asking on an Islamic based forum. If you feel laziness while doing acts of good,than that is from the devil. If you have lack of sleep,you should sleep late at one night and wake up early,the next night you will be asleep before you know it and that will get rid of your sleeping problem(that is,if you have one). If you feel lazy,I would recommend you do the following,note that these options are a rough guideline that is to be used in a proper way. These options can be used when you are lazy during worship,good deeds or even anything else(example:late night shifts;here:
What to do when you feel lazy during the act of good:
•Dhikr to Allah
•Make dua to Allah
•Straighten your intention of pleasing your lord.
•Drink coffee(to stay awake)
•Repent on all your previous sins
•Reflect on yourself
•Pray 2 Nafil prayers(or more)
That is all I can think of right now,insh'allah I'll add more.
